1. Field of the Invention
The invention relates to an apparatus to produce coated paper, cardboard or other fibrous webs with at least one thermo-sensitive layer as a functional layer through the application of at least one liquid or paste-like thermo-sensitive coating medium onto a carrier web by way of a unit which forms a functional layer. The invention also relates to a method to operate an apparatus to produce coated paper, cardboard or other fibrous webs with at least one thermo-sensitive layer. The invention is also suitable for other webs that are suitable for recording mediums, such as films or textile substrates which are to be given a thermo-sensitive layer on one or both sides.
2. Description of the Related Art
A thermal sensitive or thermo-sensitive layer is to be understood to be a coating layer which, under the effect of heat, especially through contact with a heatable printing head, is suitable to provide an image of visually recognizable information by way of a color change. This may involve at least one color generator, one color developer and a fixing agent. Apparatuses to produce coated paper, cardboard or other fibrous webs with at least one thermo-sensitive layer in the form of thermo papers through the application of a liquid or paste-like thermo-sensitive coating medium onto a carrier web by way of a curtain coater are already known for example from                La papeterie 275, April-May 2006, pages 6-14 and        Revue de Papier Carton #85, February-March 2006, pages 34-37        
Here, a dryer section is located after the applicator device which is in the embodiment of a curtain coater. In order to avoid curling, water is applied to the backside to improve laying flat. With this type of basic configuration a single thermo-sensitive layer can be applied. Further developments in the area of thermo papers and the expansion of the scope of application have led to the development of high quality thermo papers. These are coated either on both sides with one thermo-sensitive coating or feature a cover layer as a protective layer over the thermo-sensitive layer. In order to achieve these additional functional layers, units which form functional layers are to be provided in accordance with the number of individual layers. These units comprise applicator devices with coating medium supply systems allocated to them, followed by a drying section in order to ensure the required dry content. Such devices are however characterized by a considerable space requirement and, because of the multitude of functional layer forming units, are cost intensive. However, depending upon the type of coated fibrous web that is to be produced, individual applicator devices and the following drying sections are not required, so that over capacities exist over large parts of the entire operational area and the apparatus is not utilized to its optimum.
What is needed in the art is an apparatus to produce coated paper, cardboard or other fibrous webs, especially in the form of thermo papers, so that the disadvantages existing in the current state of the art are avoided. The apparatus should be characterized by a simple construction with few components and should be capable of coating one carrier web several times on one side, especially twice, or capable of coating it on both sides with at least one coating. Change-over to run the different types of coated paper, cardboard or other fibrous webs is to be simple and involve few control changes and should be possible in a timely manner, without conversion measures to meet current demands.